Satellite Shot Offers Navy Key Space Defense Trial: How It Works

The Pentagon today announced that a Navy warship has been tasked with shooting down a failing United States spy satellite that, if left alone, was expected to hit Earth within weeks.

In a joint news conference, NASA administrator Michael Griffin and Gen. James Cartwright, the No. 2 officer at the Defense Department, announced that an SM-3 missile, designed to hit inbound ballistic missiles, will be fired from a Navy cruiser or destroyer during the next month to obliterate the inbound spacecraft. The idea is to break apart the satellite to rid it of toxic fuel onboard by smashing its tank, which is the largest intact piece left. If successful, it would be the first direct U.S. test against a satellite since 1985, when an F-15 climbed to 80,000 ft. to fire a three-stage missile at a defunct solar-monitoring platform in low-Earth orbit.

A growing number of guided missile cruisers­ are fitted with Aegis Ballistic Missile Defense systems that are designed to track and destroy short- and medium-range ballistic missiles just outside Earth's atmosphere. The powerful radars on board the ships that detect ballistic missiles can also spot satellites at low orbits. Reportedly, one of three cruisers will have a shot at the inbound satellite.

Several successful anti-ballistic mile tests have been conducted from the cruisers, most frequently from the USS Shiloh, but no test has the urgency or high profile as the impending satellite shoot-down. The SM-3, when fired vertically, can target a satellite as high as 310 miles. After the third stage of the rocket is spent, the kill vehicle finds the target with forward-looking infrared sensors and steers itself into the satellite. "What we're talking about is a minor modification in software, from the Aegis system and the missile itself," Cartwright said.

The Bush administration has made ballistic missile defense a priority, fielding various interceptors at bases in Alaska and on ships. Although the odds were in favor of the satellite crashing in the ocean and/or losing much of the sensitive equipment during a fiery reentry, the chance to use the ballistic defenses against a real-life target was likely considered too good to pass up.

The operation is reminiscent of last year's strike by the Chinese military against one of its defunct spy satellites. However, the impact of the Chinese test produced a halo of space junk that remains in orbit. The U.S. Navy strike should only leave debris that will burn up harmlessly during reentry. Also, the Chinese test left debris that will last decades due to its higher orbit, Griffin said. The lower in orbit that the Navy can shoot down the satellite, the quicker debris gets pulled back in to the atmosphere. Griffin said the debris should be cleared out of Earth's orbit within weeks.

The Chinese and U.S. tests are also similar in that both strikes use rockets (in China's case, reportedly a four-stage rocket instead of the SM-3's three stages) to take a non-explosive warhead into low-Earth orbit and steer it into the target. Ways to knock out satellites at high altitudes—like communications satellites soaring at over 20,000 miles—are more esoteric and largely untested. Most high-orbit methods would require weapons already launched into orbit.

The target spacecraft is reportedly a spy satellite that launched on a Delta II rocket at Vandenberg Air Force Base in December 2006, but failed within minutes after the launch. After a fiery reentry, tens of pounds of material would be left—posing a small but real risk of landing in a populated area. The likelihood of gathering usable intelligence from the crash is thought to be minimal, since its antennae and sensors would be among the most fragile components—and would not likely survive the heat of reentry. The craft's fuel, however, is considered toxic. "[We want to] get rid of the hydrazine and have it land in the ocean," Cartwright said. "That is the only thing that breaks it out and makes this different."

That could be worrisome, because predicting exactly where the satellite will land has to wait until reentry begins. Cartwright and Griffin said NASA and the military could get a quadrant of the impact, but would not know the location of the impact until it was too late. "Nothing we can do makes it worse, and almost everything we do would make it better," Griffin said.

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